1. Field of the Invention
The present invention relates to a multilayer electronic part which composes an inductor formed by superposing coil conductors and magnetic or nonmagnetic material, and a filter, resonator etc. formed by interposing a capacitor on the inductor, and a producing method thereof.
2. Description of the Related Art
Conventional multilayer electronic parts are produced by the following manner. As shown in FIG. 10A illustrating a layer structure, sheets 1 which are made of a magnetic or nonmagnetic material and which each has a coil conductor 2 formed thereon and further has a through-hole 3 formed therein are superposed on one another. The resultant assemblage is burned and then cut into chips. As shown in FIG. 11A, these chips 4 are press-fitted into holes 5a formed in a supporting plate 5, e.g., a silicon plate, and then dipped on both sides into a silver paste 6. After these chips 4 are baked, they are electroplated with, e.g., nickel or tin to form terminal electrodes 7. In the thus-produced conventional electronic parts, the two terminal electrodes 7 are located respectively on both ends along a direction perpendicular to the direction X of the magnetic flux which generates when current is caused to flow through the coil 40, as shown in FIG. 10B. In addition, each terminal electrode 7 necessarily has a part 7a which extends beyond the edges and covers those parts of the sides which are located close to the end.
However, the electronic parts having the constitution described above have the following problem. When this electronic part 10 is mounted on a printed board 9, the resultant magnetic circuit including the printed board 9 changes in magnetic resistance and other properties depending on whether the electronic part 10 is mounted so that the direction of magnetic flux X is perpendicular to the plane of the printed board 9 as shown in FIG. 10C, or is mounted so that the direction of magnetic flux X is parallel to the plane of the printed board 9 as shown in FIG. 10D. This property change, attributable to the manner in which the electronic part 10 is-mounted on the printed board 9, is remarkable especially when the electronic part 10 is used, e.g., as a small inductor for high frequencies which employs a material having a low permittivity.
In order to eliminate the problem described above, JP-A-8-55726 discloses an electronic part having terminal electrodes 7 which have been formed in a later step by dipping and are located respectively on both ends along the direction of the magnetic flux generating when current is caused to flow through the coil conductors in the multilayer structure, as shown in the sectional view of FIG. 11B and the slant view of FIG. 11C. (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined Japanese patent publicationxe2x80x9d.)
However, the multilayer electronic parts having terminal electrodes 7 formed in a post-step have the following problems. Since the distance L1 between the terminal electrodes 7 considerably fluctuates as shown in FIG. 11D, not only considerable property fluctuations and a poor yield result, but also the terminal electrodes 7 are apt to have defects such as a projection 7b called a horn. Because of such defects, the dimension L2 fluctuates. Consequently, when electronic parts 10 which have been stored in bulk are transported through a channel 11 having a width suitable for the dimension of the electronic parts 10, as shown in FIG. 11 E, and mounted in a row, there are cases where some electronic parts 10 incline due to the presence of the projection 7b and are mounted in the inclined state on a printed board 9.
It is an object of the present invention to provide an electronic part which is reduced in property fluctuations when being mounted on a printed board, has improved accuracy with respect to the distance between the terminal electrodes thereof and to the dimension thereof to thereby attain an improved yield, and can be satisfactorily mounted after storage in bulk.
It is another object of the present invention is to provide a method for producing the electronic part.
A multilayer electronic part having the shape of a substantially rectangular parallelopiped, according to the present invention is comprised of coil conductors; sheets each comprising a magnetic or a nonmagnetic material, the coil conductors and the sheets being stacked to form a coil in the multilayer electronic part; and terminal electrodes provided on both ends of a multilayer body in which the coil conductors and the sheets are stacked along a direction of a magnetic flux generating when current is applied to flow through the coil conductors in the multilayer body, the terminal electrodes being formed of a conductive layer structure member of the multilayer body.
In the multilayer electronic part according to the present invention, the terminal electrode is formed on only both end surfaces of the multilayer structure and projects to the side surfaces. Accordingly, fluctuations in terminal electrode distance due to the protruded portions from the end surface to the side surface is eliminated. As the result, fluctuations in its property can be reduced. In addition, since the terminal electrode is a component of the conductive layer structure member of the lamination bodies, the multilayer electronic part is free from the projection generated in the dipping method, and is improved in dimensional accuracy. Further, in an automatic machine for mounting the electronic parts on printed boards or the like, they can be arranged in a row in a channel of the machine and can be mounted on the substrate without inclination.
In the producing method of the multilayer electronic parts according to the present invention, the terminal electrode is formed simultaneously with cutting the lamination bodies.